This invention relates to a specific piezoelectric (P.E.) voltage generator means, specifically a hammer that can be gravity driven or mechanically driven to apply high compressive stress to two or more P.E. crystals that are located adjacent to or in close proximity to a fixed anvil means wherein the voltage generated is transferred to a gas filled discharge tube with high impedance to produce visible light.
Conventionally, the energy for ignition of lights including flash lamps used in portable photographic equipment is obtained from batteries installed in the flashgun or camera. However, batteries are not entirely satisfactory since they deteriorate with use and time, and must be replaced at relatively frequent intervals. Piezoelectric generators have been proposed as a replacement for batteries since they are capable of producing a large amount of energy, have a life commensurate with the rest of the camera and remain relatively stable in performance without significant loss of voltage or electrical capacity.
In a system disclosed in the prior art (U.S. Pat. No. 3,808,418 issued to Conard et al) a piezoelectric crystal is mechanically stressed and the energy produced is used to excite a neon filled tube. This system produces low voltage and extremely low power. This system is neither appropriate to nor capable of producing the high voltage and power regime required for the subject invention. The mechanical means for stressing the crystals is also completely distinct from the structure claimed herein.
Another known method involves using sheets of piezoelectric material arranged as a flexible cantilevered beam structure. When the unsupported end of the beam is displaced and released, the beam rebounds momentarily, touching an electrical contact at the point of maximum beam displacement. The piezoelectric material is delivered to the lamp when the beam rebounds and contacts the lamp terminals. This method requires a large, bulky enclosure to permit the movement of the beam.
Flash-firing mechanism which include a piezoelectric generator for triggering an electronic flash unit are also known in the art. For example, U.S. Pat. No. 2,972,937 issued to C. G. Suits on Feb. 28, 1961, entitled Flash Apparatus discloses a piezoelectric crystal arranged to produce a high voltage impulse to fire a photoflash lamp in timed relation to light-unblocking movement of a camera shutter.
U.S. Pat. No. 3,782,258 issued to Boekkooi et al on Jan. 1, 1974, entitled Ignition Arrangement For a Discharge Tube discloses a piezoelectric generator coupled to an electronic flash unit to initiate conduction of the Xenon in the flashtube. In one embodiment disclosed therein, the piezocrystal output pulse is applied directly to the trigger electrode of the flashtube. In an alternative embodiment, the P.E. crystal pulse is applied to the gate electrode of an silicon controlled rectifier which is turned on to complete a conventional trigger circuit to energize the flashtube.
It has been found that the application of a piezo impulse directly to a flashtube trigger electrode as is done in the first embodiment disclosed in the Boekkooi et al patent does not always operate to fire the flashtube. This is despite the relatively high amplitude of the piezo pulse which may be several thousand volts. It has been theorized that due to the relatively short duration of this pulse, which may be on the order of approximately 5 microseconds or less, the flashtube interelectrode resistance is not sufficiently reduced. When this results, the flash-firing capacitor fails to discharge through the flashtube and a flash does not occur.
In the other embodiment disclosed in the Boekkooi et al patent, the conventional flash-trigger circuit comprises a trigger capacitor, which may be charged to several hundred volts, in parallel with a trigger electrode transformer, the primary winding of which is in series with the aforementioned SCR. This circuit avoids the problem referred to hereinbefore associated with a direct application of the piezo pulse to the triggger electrode.
Accordingly, the inventor has invented an improved mechanism that may be gravity driven or spring driven to produce electrical current by applying sharpely impacted compression on one or more P.E. crystals and transferring that current directly to a gas filled discharge tube having high impedance to produce visible light.